Permanent magnet rotor of brushless motor

ABSTRACT

A brushless motor includes a stator and a rotor rotatably supported within the stator. The rotor includes a yoke which is formed by laminating many steel sheets so as to provide an even number of magnetic poles projected externally and slots provided in each of or every other said magnetic poles, a permanent magnet for a field inserted in each of said slots and having top, bottom, front, rear, and side faces, and protuberances provided on opposite sides of said slots and brought into contact with the side faces of said permanent magnet for the field, forming spaces on opposite sides of said slots.

TECHNICAL FIELD

This invention relates to a permanent magnet rotor of a brushless motor,and particularly to a permanent magnet rotor of a brushless motor whichhas a yoke made by laminating a large number of steel sheets, an evennumber of magnetic poles protruding outward on the yoke, and a permanentmagnet for a field inserted in each magnetic pole or every othermagnetic poles.

BACKGROUND ART

Generally known brushless motors consist of a permanent magnet rotorwhich has a plurality of permanent magnets for a field inserted in ayoke made by laminating steel sheets and a stator which has magneticpoles opposing to the outer periphery of magnetic poles of the abovepermanent magnet rotor with a small space therebetween.

FIG. 35 is a sectional view in a direction intersecting at right angleswith the rotatable shaft of a brushless motor using a conventionalpermanent magnet rotor. In this drawing, a conventional brushless motor51 consists of a stator 52 and a permanent magnet rotor 53. The stator52 has the permanent magnet rotor 53 rotatably supported therein andmany stator magnetic poles 54 protruded inward. The stator magneticpoles 54 have a coil (not shown) wound thereon. Passing a currentthrough the coil excites a prescribed magnetic pole of the statormagnetic poles 54. A magnetic pole face 55 at the end of the statormagnetic poles 54 is positioned above a cylindrical face at an equaldistance from the center of a rotatable shaft 56 of the motor.

The permanent magnet rotor 53 consists of a yoke 57 made by laminatingmany steel sheets and a pair of permanent magnets 58 for a field. Theyoke 57 has four magnetic poles 59 protruded externally on its outerperiphery, and the permanent magnets 58 for the field are inserted inevery other bases of the magnetic poles 59 with N poles opposed to eachother. A magnetic pole face 60 at the end of each magnetic pole 59 isformed to have a curved shape at an equal distance from the center ofthe rotatable shaft 56, and opposed to the magnetic pole face 55 at anequal distance at every point on the face of the rotatable magnetic poleface 60.

In the above permanent magnet rotor 53, the repulsion of the N poles ofthe permanent magnets 58 for the field causes the magnetic fluxes to getout of the magnetic pole faces 60 without the permanent magnet for thefield as shown in the drawing, to pass through the stator, and to enterthe yoke 57 from the magnetic pole faces 60 with the permanent magnetfor the field. Accordingly, the magnetic poles having the permanentmagnet of the permanent magnet rotor 53 become S pole, and those nothaving the permanent magnet of the permanent magnet rotor 53 become Npole.

As shown in the drawing, the permanent magnet rotor 53 is rotated byexciting the stator magnetic poles 54, which have been slightly deviatedin the rotating direction from the center of the magnetic poles 59 ofthe permanent magnet rotor 53, to N pole. The permanent magnet rotor 53is rotated by being attracted to the excited stator magnetic poles 54.Then, the stator magnetic poles 54 which are further displaced withrespect to the rotated permanent magnet rotor 53 are excited to N pole.The permanent magnet rotor 53 is further rotated by being attracted tothe newly excited stator magnetic poles 54. This procedure is repeatedto continuously rotate the permanent magnet rotor 53.

The known conventional brushless motor uses a back electromotive forcegenerated by the rotation of the permanent magnet rotor 53 to determinethe position of the above permanent magnet rotor. Specifically, therotation of the permanent magnet rotor 53 causes the magnetic fluxes ofthe permanent magnets 58 for the field to cross the coils (not shown)wound on the magnetic pole faces 55 of the stator 52 to generate theback electromotive force in the coils of the stator 52. The position ofthe back electromotive force is detected to detect the position of eachpermanent magnet for a field of the permanent magnet rotor 53, and theposition of the magnetic poles to be excited on the stator side isdetermined and excited.

FIG. 36 shows a conventional permanent magnet rotor in an explodedstate. A conventional permanent magnet rotor 53 has a yoke 57 andpermanent magnets 58 for a field. The yoke 57 is formed by laminating alarge number of steel sheets 61. The yoke 57 has magnetic poles 57formed on the outer periphery, and at the bases of the magnetic poles59, slots 62 are respectively formed to insert the permanent magnets 58for the field. Furthermore, each steel sheet 61 is pressed to formcaulking sections 63 recessed in the form of a rectangle. The steelsheets 61 are integrally laminated by mutually press-fitting thecaulking sections 63.

The permanent magnets 58 for the field are formed to a size capable ofbeing housed in the slots 62. In assembling the permanent magnet rotor53, an adhesive is applied to the surfaces of the permanent magnets 58for the field, which are then inserted in the slots 62 with their samemagnetic poles opposed to each other as shown in the drawing. Arrows Qin the drawing indicate the directions that the permanent magnets 58 forthe field are inserted.

On the other hand, for the permanent magnet rotor 53 which cannot use anadhesive because of its application conditions, the permanent magnets 58for the field are formed so as to be fitted in the slots 62 withoutleaving any gap. To assemble the permanent magnet rotor 53, thepermanent magnets 58 for the field are pushed in the directions Q shownin the drawing by a pneumatic device so as to be forced into the slots62. Therefore, a force is applied, in centrifugal directions R, tobridges 64 connecting the leading end of the magnetic pole and the baseof the magnetic pole at both ends of the slot.

FIG. 37 shows a permanent magnet rotor in an exploded state developed bythe present applicant. It is shown that engagement pawls 62a are formedto protrude to engage with a permanent magnet 58 for a field on theinner periphery of slots 62 for inserting the permanent magnet for thefield. The permanent magnet 58 for the field can be inserted in theslots 62, and has a sectional shape to engage with the engagement pawls62a.

With the above permanent magnet rotor, the permanent magnet 58 for thefield is engaged with the engagement pawls 62a only and its frictionalresistance is small, allowing to press-fit the permanent magnet 58 forthe field into the yoke 57 by a small pressing force. And, when thepermanent magnet 58 for the field is press-fitted into the yoke 57, theengagement pawls 62a can hold the permanent magnet 58 for the field toprevent it from coming out.

In the above prior arts, the permanent magnet rotors which apply anadhesive to the outer periphery of the permanent magnets for the fieldbefore inserting in the slots of the yoke have disadvantages that theadhesive is dissolved with a refrigerant or pressurizing fluid and thepermanent magnets for the field come out.

On the other hand, in the conventional permanent magnet rotor whichdirectly forces the permanent magnets for the field into the slots ofthe yoke without using an adhesive, a large force is used to press-fitthe permanent magnets for the field, and this force sometimes breaks thepermanent magnets for the field, or an inserting force is applied to thebridges in the centrifugal directions, possibly resulting in theirbreakage. And, the above permanent magnet rotor is required to have ahigh processing precision for fitting the permanent magnets for thefield in the slots of the yoke in view of a dimensional tolerance,making it difficult to produce the permanent magnet rotor. Besides, theintimate contact of the permanent magnets for the field with the bridgesat both ends of the slots causes the magnetic fluxes of the permanentmagnets for the field to leak at the bridges and prevent them frompassing the outside space of the magnetic poles, resulting in no crossof the magnetic fluxes with the stator of a motor. Therefore, themagnetic fluxes do not produce a force for rotating the permanent magnetrotor. And, the leakage of the magnetic fluxes at the bridges generatesheat due to a core loss.

In view of the above, an object of this invention is to provide apermanent magnet rotor which prevents the permanent magnets for thefield from being come out due to a refrigerant or pressurizing fluid,makes positioning of the permanent magnets for the field, can beproduced easily, and has high performance.

And, the permanent magnet rotor (see FIG. 37) invented by the applicanthas an advantage that a force for press-fitting the permanent magnetsfor the field is reduced extensively. But, the engagement pawls of eachsteel sheet are gradually bent in the press-fitting direction when thepermanent magnet for the field is press-fitted, this bending of theengagement pawls is accumulated to heavily bend the engagement pawls atthe end in the laminating direction of the yoke, and this bendingexceeds a binding force of the caulking sections of the steel sheets topartly separate the steel sheets. Besides, in a conventional permanentmagnet rotor, because of different tolerances of the permanent magnetfor the field and the yoke length in the axial direction, the leadingend of the permanent magnet for the field does not completely engagewith the engagement pawls of the steel sheets at the end of the yokewhen the permanent magnet for the field is shorter than the yoke,resulting in an unstable press-fitted state and sometimes separating thesteel sheets due to vibration or the like.

Accordingly, another object of this invention is to remedy the unsolvedproblems of the permanent magnet rotor invented by the present applicantand to provide a permanent magnet rotor of a brushless motor in whichthe permanent magnet for the field can be inserted by a small pressingforce and prevented from coming out, and the steel sheets at the end ofthe yoke are not separated when press-fitting the permanent magnet forthe field and using, and to provide a method for producing it.

Furthermore, in the above permanent magnet rotor (see FIG. 37) inventedby the applicant, part of the magnetic fluxes of the permanent magnetfor the field getting out from the N poles passes through the bridges ofthe yoke to reach the P poles of the permanent magnet for the field. Themagnetic fluxes passing through the bridges do not cross the stator of amotor and do not contribute to rotate the permanent magnet rotor.Therefore, the efficiency of the magnetic force of the permanent magnetsfor the field is lowered in inverse proportion to the magnetic fluxes ofthe permanent magnets for the field passing through the bridges.

On the other hand, the reduction of the sectional areas of the bridgesof the yoke can reduce the number of magnetic fluxes passing through thebridges. This is because the number of magnetic fluxes passing throughthe bridges is determined from the product of a flux density determinedaccording to the yoke material by a sectional area of the bridges.

But, in the yoke formed by laminating the steel sheets, the steel sheetsforming the yoke are generally formed by a punch-out process, but it isquite difficult to punch out the steel sheets for the yoke having thebridges with a very small sectional area. Besides, in the yoke havingthe bridges with a very small sectional area, the bridges of the yokeare required to have a high mechanical strength because the magneticpoles and the permanent magnets for the field suffer from a centrifugalbreakage due to the centrifugal force when the yoke is rotated at a highspeed. And when the bridges have a high mechanical strength, there is adisadvantage that the utilization efficiency of the permanent magnetsfor the field is lowered.

In view of the above, another object of this invention is, in apermanent magnet rotor of a brushless motor having permanent magnets fora field, to provide a permanent magnet rotor which forms a yoke by aplurality of steel sheets laminated, and has an optimum bridge width ofthe yoke among a width which can be punched out, a width allowable inview of the number of passing magnetic fluxes, and a width allowable inview of a mechanical strength by a centrifugal force.

Besides, in a conventional permanent magnet rotor, the magnetic fluxesof the permanent magnets for the field are concentrated on a positiondeviated in the rotating direction from the circumferential center ofthe magnetic poles due to the relation between the bridge width and thewidth in a radial direction at the magnetic poles, or the relativepositional relation of the permanent magnet rotor and the stator of thebrushless motor, the back electromotive force generated by the magneticfluxes is detected earlier than the actual position of the permanentmagnets for the field, the magnetic poles of the stator are excitedearlier than a prescribed timing, and the permanent magnet rotor has afailure in its rotation.

In view of the above, another object of the invention is to provide apermanent magnet rotor which is formed to concentrate the magneticfluxes of a magnet for a field to a prescribed position of a magneticpole and can accurately detect the position of the magnetic pole.

SUMMARY OF THE INVENTION

In a brushless motor comprising a stator and a rotor rotatably supportedwithin the stator, wherein the rotor has a yoke which is formed bylaminating many steel sheets, the yoke has an even number of magneticpoles protruded externally, and a permanent magnet for a field isinserted in each magnetic pole or every other magnetic poles, thisinvention is to provide a permanent magnet rotor characterized by thatthe above permanent magnet for the field is inserted in slots formed onthe magnetic poles, and the slots are provided with protrusions at bothends to come in contact with the side faces of the permanent magnet forthe field.

And, in a brushless motor comprising a stator and a rotor rotatablysupported within the stator, wherein the rotor has a yoke which isformed by laminating many steel sheets, the yoke has an even number ofmagnetic poles protruded externally, and a permanent magnet for a fieldis inserted in each magnetic pole or every other magnetic poles, thisinvention is to provide a permanent magnet rotor characterized by thatthe above permanent magnet for the field is inserted in slots formed onthe magnetic poles, the slots have engagement pawls disposed to protrudeso as to engage with the permanent magnet for the field, and among thelaminated steel sheets of the yoke, those corresponding to theengagement pawls have reliefs for absorbing a bend of the engagementpawls.

And, in a brushless motor comprising a stator and a rotor rotatablysupported within the stator, wherein the rotor has a yoke which isformed by laminating many steel sheets, the yoke has an even number ofmagnetic poles protruded externally, and a permanent magnet for a fieldis inserted in each magnetic pole or every other magnetic poles, thisinvention is to provide a permanent magnet rotor characterized by thatat least one end of the yoke has a steel sheet deviated in a rotatingdirection.

And, in a brushless motor comprising a stator and a rotor rotatablysupported within the stator, wherein the rotor has a yoke which isformed by laminating many steel sheets, the yoke has an even number ofmagnetic poles protruded externally, and a permanent magnet for a fieldis inserted in each magnetic pole or every other magnetic poles, thisinvention is characterized by that the above permanent magnet for thefield is inserted in slots formed on the magnetic poles, and a bridgewidth at either end of the slots is determined, among a width which canbe punched out, a width allowable in view of the number of passingmagnetic fluxes, and a width allowable in view of a mechanical strengthby a centrifugal force, to be a larger one between the width which canbe punched out and the width allowable in view of the mechanicalstrength by the centrifugal force.

And, in a brushless motor comprising a stator and a rotor rotatablysupported within the stator, wherein the rotor has a yoke which isformed by laminating many steel sheets, the yoke has an even number ofmagnetic poles protruded externally, and a permanent magnet for a fieldis inserted in each magnetic pole or every other magnetic poles, thisinvention is to provide a permanent magnet rotor characterized by thateach magnetic pole has at least one connecting portion or gap forlaminating the steel sheets.

And, in a brushless motor comprising a stator and a rotor rotatablysupported within the stator, wherein the rotor has a yoke which isformed by laminating many steel sheets, the yoke has an even number ofmagnetic poles protruded externally, and a permanent magnet for a fieldis inserted in each magnetic pole or every other magnetic poles, thisinvention is to provide a permanent magnet rotor characterized by thatthe above permanent magnet for the field is inserted in slots formed onthe magnetic poles, and a bridge width at either end of the slots isdisposed to be smaller than a width between the outside of the permanentmagnet for the field and the outside edge of the magnetic pole.

And, in a brushless motor comprising a stator and a rotor rotatablysupported within the stator, wherein the rotor has a yoke which isformed by laminating many steel sheets, the yoke has an even number ofmagnetic poles protruded externally, and a permanent magnet for a fieldis inserted in each magnetic pole or every other magnetic poles, thisinvention is to provide a permanent magnet rotor characterized by that awidth of the magnetic pole in a radial direction is about 1.5 times of apole width of the stator.

Furthermore, in a brushless motor comprising a stator and a rotorrotatably supported within the stator, wherein the rotor has a yokewhich is formed by laminating many steel sheets, the yoke has an evennumber of magnetic poles protruded externally, and a permanent magnetfor a field is inserted in each magnetic pole or every other magneticpoles, this invention is to provide a permanent magnet rotorcharacterized by that the front or back of the outer periphery and in arotating direction of the magnetic pole is notched to a certain shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the permanent magnet rotor in anexploded state of this invention.

FIG. 2 is a sectional view showing the permanent magnet rotor of thisinvention.

FIG. 3 is a sectional view of an essential part showing anotherembodiment of this invention.

FIG. 4 is a perspective view showing the permanent magnet rotor in anexploded state of another embodiment of this invention.

FIG. 5 is a sectional view of the center in the laminated direction ofthe permanent magnet rotor of this invention.

FIG. 6 is a sectional view of the end in the laminated direction of thepermanent magnet rotor of this invention.

FIG. 7 is a sectional view showing the permanent magnet rotor in apartly enlarged state of this invention.

FIG. 8 is a view showing the process for punching out a steel sheet forthe permanent magnet rotor of this invention.

FIG. 9 is a sectional view showing a punch die used in this invention.

FIG. 10 is a perspective view showing the permanent magnet rotor in anexploded state of this invention.

FIG. 11 is a sectional view of the permanent magnet rotor of thisinvention.

FIG. 12 is a sectional view of the steel sheet of this invention turnedin a rotating direction by m°.

FIG. 13 is a sectional view of the steel sheet of this invention turnedin a rotating direction by m°.

FIG. 14 is a sectional view of the permanent magnet rotor of thisinvention.

FIG. 15 is a sectional view of the permanent magnet rotor of thisinvention.

FIG. 16 is a perspective view showing the permanent magnet rotor in anexploded state of another embodiment of this invention.

FIG. 17 is a sectional view of the permanent magnet rotor of anotherembodiment of this invention.

FIG. 18 is a perspective view of the permanent magnet rotor of anotherembodiment of this invention.

FIG. 19 is a perspective view of the permanent magnet rotor of anotherembodiment of this invention.

FIG. 20 is a perspective view of the permanent magnet rotor in anexploded state of another embodiment of this invention.

FIG. 21 is a sectional view of the permanent magnet rotor of anotherembodiment of this invention.

FIG. 22 is a perspective view of the permanent magnet rotor of anotherembodiment of this invention.

FIG. 23 is a sectional view of the permanent magnet rotor of anotherembodiment of this invention.

FIG. 24 is a graph showing a relation among the bridge width, themagnetic flux density of the bridges, and the mechanical strength of thebridges.

FIG. 25 is a perspective view of the permanent magnet rotor of anotherembodiment of this invention.

FIG. 26 is a sectional view of the permanent magnet rotor of anotherembodiment of this invention.

FIG. 27 is a front view of the yoke of the permanent magnet rotor ofthis invention.

FIG. 28 is a sectional view of the yoke of the permanent magnet rotor ofthis invention.

FIG. 29 is a computer-analyzed diagram showing the flow of magneticfluxes on a cross section intersecting at right angles to the rotatableshaft of the permanent magnet rotor of a three-phase, four-pole motor ofthis invention with the rotor rotating satisfactorily.

FIG. 30 is a computer-analyzed diagram showing the flow of magneticfluxes on a cross section intersecting at right angles to the rotatableshaft of the permanent magnet rotor of a three-phase, four-pole motor ofthis invention with the rotor rotating.

FIG. 31 is a computer-analyzed diagram showing the flow of magneticfluxes on a cross section intersecting at right angles to the rotatableshaft of the permanent magnet rotor of a three-phase, four-pole motor ofthis invention with the rotor rotating.

FIG. 32 is a graph showing a gap magnetic flux density.

FIG. 33 is a graph showing a gap magnetic flux density.

FIG. 34 is a diagram showing a relation between the permanent magnetrotor and the stator.

FIG. 35 is a sectional view showing a conventional permanent magnetrotor and stator.

FIG. 36 is a perspective view showing a conventional magnet rotor in anexploded state.

FIG. 37 is a perspective view showing a conventional magnet rotor in anexploded state.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows the permanent magnet rotor in an exploded state of thisinvention. A permanent magnet rotor 1 has a column yoke 2 and a pair ofplate permanent magnets 3, 3 for a field. The yoke 2 is formed bylaminating a large number of steel sheets 4, 4 into one body. The yoke 2has four magnetic poles 5 (5a, 5b, 5c and 5d) protruding outwardradially formed on the outer periphery. Among these magnetic poles, thetwo magnetic poles 5a, 5c opposing to each other have at their bases apair of slots 6, 6 for inserting the permanent magnet 3 for the field.Furthermore, at the center of the yoke 2, a hole 7 is formed to pass arotatable shaft (not shown) through it. The steel sheet 4 has its partrecessed to form caulking sections 8, 8, and the caulking sections 8 aremutually press-fitted to laminate into one body.

The steel sheet 4 forming the slots 6, 6 has at both ends of the slotsformed a plurality of protuberances 9, 9 in the shape of a triangle.

The permanent magnets 3, 3 for the field are formed into a hexahedronhaving a rectangular cross section, and respectively inserted into theslots 6, 6 in the directions P shown in the drawing so that the faceshaving the magnetism of N pole are faced to the hole 7.

FIG. 2 is a sectional view of a permanent magnet rotor, showing a crosssection in a direction intersecting at right angles to the rotatableshaft of the yoke 2. The slots 6, 6 are bases of the magnetic poles 5a,5c of the yoke 2 and disposed at substantially equal distance from therotatable shaft. The permanent magnets 3, 3 for the field are disposedwith their faces having the magnetism of N pole opposed to each other,and the magnetic fluxes get out of the magnetic poles 5a, 5c of the yoke2 by the repulsion of the magnetic poles and reach the magnetic poles5b, 5d as shown in the drawing. As a result, the magnetic poles 5a, 5cshow the magnetism of S pole, and the magnetic poles 5b, 5d show themagnetism of N pole. Thus, the outer periphery of the yoke 2 has fourmagnetic poles which have N and S poles alternately.

Furthermore, either end of the slot 6 has a bridge 10 to connect thebase and the leading end of the magnetic pole 5, and there is a spacebetween the bridge 10 and the permanent magnets 3, 3 for the field, sothat the magnetic fluxes from the N pole side of the permanent magnetsfor the field pass through the bridges 10 to reach the S pole side ofthe permanent magnets for the field, but the magnetic fluxes passingthrough the bridges 10 are reduced because of a large distance from thepermanent magnets for the field.

As shown in the drawing, the permanent magnets 3, 3 for the field havetheir surfaces partly engaged with one side of the protuberances 9 whenpress-fitted, and the protuberances 9 suffer from deflection or plasticdeformation in the outward directions R due to a dimensional differenceof the magnets and are held within the slots 6, 6. The protuberances 9prevent the permanent magnets 3, 3 for the field from contacting to thebridges 10 and the inner periphery of the slots 6, 6 on the side of therotatable shaft. Therefore, the friction due to the contact between thepermanent magnets 3, 3 for the field and the slots 6, 6 is small, andthe permanent magnets for the field can be inserted by a small force andpositioned. As shown in the drawing, when press-fitted, the outerperiphery of the permanent magnets 3, 3 for the field engages with oneside of the protuberances 9 to prevent the permanent magnets 3, 3 forthe field from coming out, and no extra force is applied to the bridges10. Since the permanent magnet rotor of this invention does not use anadhesive to hold the permanent magnets 3, 3 for the field in the slots6, 6, the permanent magnets 3, 3 for the field can be prevented fromcoming out even when the permanent magnet rotor is used in a refrigerantor pressurizing fluid because the adhesive does not dissolve in therefrigerant or pressurizing fluid. Besides, the permanent magnets forthe field can be fixed regardless of the processing precision of thepermanent magnets for the field.

FIG. 3 shows the yoke of another embodiment of the permanent magnetrotor of this invention.

In this embodiment, protuberances 9 of the steel sheet 4 has a hornshape to engage with the permanent magnet for the field (not shown) anda notch 11 disposed on one side of the bottom of the horn shape of theprotuberances 9. The protuberances 9 are connected to the inner edge ofthe steel sheet 4 forming the slot 6 via the notch 11. To engage withthe permanent magnet for the field, the protuberances 9 must be inclinedto a prescribed level. When the protuberances 9 are excessively large,the magnetic flux of the permanent magnet for the field leaks at theprotuberances 9, resulting in increasing the leaked magnetic fluxes.And, when the protuberances 9 are not inclined to the prescribed level,the protuberances 9 are deformed by press-fitting the permanent magnetfor the field. Positioning of the notch 11 on the side of the permanentmagnet for the field of the protuberances 9 secures an appropriateinclination of the protuberances 9, its appropriate deflection reduces aforce for inserting the permanent magnet for the field and eliminatesthe necessity of chamfering the horn part of the permanent magnet forthe field required in press-fitting the permanent magnet for the field.In other words, the permanent magnet for the field can be inserted inthe slots easily. Furthermore, either side of the slot has the bridge 10to connect the base and the leading end of the magnetic pole, and thereis a space between the bridge 10 and the permanent magnets for thefield, so that a base 10a of the bridge 10 can be made thick, resultingin increasing a strength of the bridge 10, and in the production,breakage of the bridge 10 is reduced as much as possible. In addition,the space provided reduces the leaked magnetic fluxes of the bridge 10due to the permanent magnets for the field and the heat generation dueto the core loss at the bridge 10 can be reduced because the base 10ahas a large area.

The above protuberances 9 engaging with the permanent magnets for thefield have been described with reference to the shape of a horn, but theshape is not limited to it, and may be formed into a round shape.

FIG. 4 shows the permanent magnet rotor 1 of a second embodiment in anexploded state. In the same way as in the first embodiment, the yoke 2is formed by laminating a large number of steel sheets 4 (4a, 4b) so asto match one another. The steel sheets 4b at the middle in the laminateddirection of the yoke 2 have engagement pawls 12 disposed to protrudefrom the inner periphery of the slots 6 so as to engage with thepermanent magnet 3 for the field. On the other hand, the several numberof the steel sheets 4a at either end in the laminated direction of theyoke 2 have reliefs 13 disposed to absorb a bend of the engagement pawls12 on the inner periphery of the slots 6 corresponding to the engagementpawls 12 of the steel sheets 4b at the middle.

FIG. 5 shows a sectional view at the middle of the yoke 2 having thepermanent magnets 3 for the field inserted. In the steel sheets 4b atthe middle in the laminated direction of the yoke 2, the engagementpawls 12 engage with the permanent magnets 3 for the field to reduce apress-fitting resistance of the permanent magnets 3 for the field andprevent them from coming out.

FIG. 6 shows a sectional view of the end portion in the press-fittingdirection of the yoke 2 having the permanent magnets 3 for the fieldinserted. The leading end of the permanent magnet 3 for the field whichis first press-fitted has the inclined faces to reduce its sectionalarea, and the steel sheets 4a at the ends of the yoke 2 in thepress-fitting direction have only the reliefs 13 on the inner peripheryof the slot 6, so that the leading end of the permanent magnet for thefield is not in contact with the inner periphery of the slot 6 of thesteel sheets 4a as shown in FIG. 6.

The operation of the permanent magnet rotor of the second embodimentwill be described based on the above structure with reference to FIG. 7.

FIG. 7 shows the yoke 2 with its part expanded, illustrating thelaminated state of the steel sheets 4b at the middle part and the steelsheet 4a at the end in the laminated direction, and the engaged state ofthe steel sheets 4a, 4b and the permanent magnet 3 for the field.

FIG. 7 shows that the permanent magnet 3 for the field is slightlyengaged with the engagement pawls 12 of the steel sheets 4b at themiddle of the yoke 2, so that the permanent magnet 3 for the field canbe press-fitted in the yoke 2 by a small pressing force with a smallfrictional resistance at the leading end of the engagement pawls 12. Itis experimentally known that when the permanent magnet for the field isbeing press-fitted, the engagement pawls 12 of each steel sheet 4b isgradually bent in the press-fitting direction due to the engagement andfriction with the permanent magnet 3 for the field, and the bends of theengagement pawls 12 are accumulated to be great at the end of the yoke2. As shown in FIG. 7, the steel sheet 4a at the end in the laminateddirection of the yoke 2 of this embodiment has the reliefs 13positionally matching the engagement pawls 12 formed on the innerperiphery of the slot 6 to absorb the bends of the engagement pawls 12,resulting in preventing the steel sheet 4a from separating. And, byinserting the permanent magnet 3 for the field, the engagement pawls 12and the permanent magnet 3 for the field are mutually engaged, enablingto prevent the permanent magnet 3 for the field from coming out.

According to this embodiment, the steel sheets 4a having the reliefs 13are laminated at the ends of the yoke 2 to make the permanent magnet 3for the field always longer than those having the engagement pawls 12 ofthe yoke 2, so that all engagement pawls 12 are completely engaged withthe permanent magnet 3 for the field to provide a stable press-fittedstate. Thus, the disadvantages of a conventional permanent magnet rotorin which some engagement pawls at the ends of the yoke do not engagewith the permanent magnet for the field, falling in an unstablepress-fitted state and causing the separation of the steel sheets byvibration or the like can be remedied.

A method for easily producing the permanent magnet rotor of thisembodiment will be described with reference to FIG. 8 and FIG. 9.

FIG. 8 shows one process for punching out the steel sheets to belaminated to form the yoke from a belt steel sheet. As shown in FIG. 8,the steel sheets 4a, 4b of this embodiment are punched out by sending abelt steel sheet material 14 through a punch die in the direction P at aprescribed pitch. Punch-out position A punches out the slots 6 havingthe engagement pawls 12 or the slots 6 having the reliefs 13, punch-outposition B punches out the rotatable shaft hole 7, and punch-outposition C punches out an outward form of the steel sheet 4a or 4b to belaminated and laminates at the same time. The steel sheet punch-outprocess of this embodiment uses a punch die which punches out the slots6 with different shapes according to a driving depth.

FIG. 9 shows the punch die which punches out the slots with differentshapes according to a driving depth. The punch die consists of a malemold 15 and a female mold 16, the male mold 15 of the punch die issupported to be vertically movable above the steel sheet material 14,and the female mold 16 of the punch die is fixed below the steel sheetmaterial 14. After the steel sheet material 14 is sent at a prescribedpitch and stopped at a prescribed position, the male mold 15 of thepunch die is brought down to punch out through the steel sheet material14 and to enter the female mold 16 of the punch die. Thus, the steelsheet material 14 is punched out into the shape of the male mold 15 ofthe punch die.

As shown in FIG. 9, the male mold 15 of the punch die of this embodimenthas different-shaped bottom and top ends, a lower part 15a has a shapeto punch out the slots 6 and the engagement pawls 12, and an upper part15b which is above the part 15a has a shape to punch out the reliefs 13.Thus, when a driving depth is in a range to the part 15a, the slots 6having the engagement pawls 12 can be punched out and, when the drivingdepth reaches the part 15b, the slots 6 having the reliefs 13 can bepunched out.

The production method of this embodiment first punches out a prescribednumber of the steel sheets 4a for one end of the yoke 2 at a drivingdepth in a range using the part 15b and laminates them, punches out thesteel sheets 4b for the middle of the yoke 2 at a driving depth in arange using the part 15a and laminates them, and punches out aprescribed number of the steel sheets 4a for the other end of the yoke 2at a driving depth in a range using the part 15b and laminates them tocomplete the production of the yoke 2.

According to the above production method, the yoke 2 which has the steelsheets 4a having the reliefs 13 at the ends and the yoke 2 which has thesteel sheets 4b having the engagement pawls 12 at the middle can becontinuously produced by the same production device, the productiondevice can be simplified, and work efficiency can be improvedextensively.

But, it is obvious that this invention is not limited to the above butcan also be applied to a permanent magnet rotor in which the permanentmagnets for the field are inserted into the yoke formed of the steelsheets having a prescribed shape.

In the above description about the production method, three punch diesare used to successively punch out one steel sheet, but it is to beunderstood that one punch die may be used to punch out steel sheets withdifferent shapes in the driving depth.

As described above, the yoke of the permanent magnet rotor according tothe second embodiment disposes the steel sheets having the engagementpawls for reducing a resistance at press-fitting of the permanentmagnets for the field and preventing them from coming out at the middlein the laminated direction, and disposes the steel sheets having thereliefs to absorb the bend of the engagement pawls at press-fitting ofthe permanent magnets for the field at the ends in the laminateddirection, to allow the press-fitting of the permanent magnets for thefield by a small pressing force. And, the steel sheets at the ends ofthe yoke are not separated by the press-fitting, and after theinsertion, the permanent magnets for the field are prevented from comingout. And, the permanent magnet rotor of this embodiment can easily setthe permanent magnets for the field to be longer than the part havingthe engagement pawls of the yoke, so that all engagement pawls engagewith the permanent magnets for the field to provide a stablepress-fitted state, and the possibility of the steel sheets from beingseparated by vibration can be reduced.

And, the method for producing the permanent magnet rotor of thisembodiment has the punch die which can punch out the steel sheets withdifferent shapes according to a driving depth, and can vary only thedriving depth to continuously produce the yoke having the steel sheetshaving the reliefs at the ends and the steel sheets having theengagement pawls at the middle by the same production device, so thatthe production device can be simplified, and the work efficiency can beimproved extensively.

FIG. 10 shows the permanent magnet rotor in an exploded state of a thirdembodiment. A permanent magnet rotor 1 has two pairs of plate permanentmagnets 3, 3 in this case. The yoke 2 is formed by punching out manysteel sheets 4 by a die and laminating in the same way as in the aboveembodiment. One end of the yoke 2 is made of a steel sheet 4' by havingthe steel sheet 4 deviated in a rotating direction. The steel sheets 4have caulking sections 8 which are formed by denting the steel sheets inpart, and the caulking sections 8 are mutually press-fitted to belaminated into one body. The permanent magnets 3, 3 for the field aremoved in the direction R shown in the drawing to be respectivelyinserted into the slots 6, 6d. Then a steel sheet 4" deviated in arotating direction with the hole 7 as the center integrally press-fittedby the caulking sections 8.

FIG. 11 shows a sectional view of the steel sheet 4. The slots 6, 6 areat bases of the magnetic poles 5a, 5b, 5c and 5d of the steel sheet 4and disposed at substantially equal distance from the rotatable shaft ofthe yoke. The permanent magnets 3, 3 for the field are respectivelyinserted in the slots 6, 6, The permanent magnets 3, 3 for the field aredisposed so that the outer periphery of the yoke 2 has the magnetisms ofN and S poles alternately. Furthermore, the steel sheet 4 has caulkingsections 8a, 8b, 8c and 8d inside of the permanent magnets for the fieldto mutually press-fit the steel sheets, and the caulking sections 8a,8b, 8c and 8d are mutually press-fitted for laminating.

Furthermore, intervals of the caulking sections 8a, 8b, 8c and 8d withrespect to the rotatable shaft are m between the caulking sections 8aand 8b, between the caulking sections 8b and 8c, and between thecaulking sections 8c and 8d; and k between the caulking sections 8d and8a, and determined to be p×m≠360° (p is the number of caulkings) andm≠k.

And, a gap 8'a is close to the caulking section 8a so as to be able tobe press-fitted with one of the caulking sections 8a, 8b, 8c and 8d, anda gap 8'b is close to the caulking section 8d so as to be able to bepress-fitted with one of the caulking sections 8a, 8b, 8c and 8d. Aninterval T (an angle with respect to the rotatable shaft) between thegap 9a and the caulking section 8a is set to be T=p×m-360° (p×m>360°),and an interval q (an angle with respect to the rotatable shaft) betweenthe gap 8'b and the caulking section 8d is set to be q=360°-p×m(p×m>360°). And, the caulking sections 8a, 8b, 8c and 8d and the gaps8'a, 8'b are on the same circumference with respect to the rotatableshaft.

FIG. 12 shows a sectional view (steel sheet 4") of the steel sheet 4deviated in a rotating direction by m°. Caulking sections 18a, 18b, 18cand 18d of the steel sheet 4" correspond to the caulking sections 8a,8b, 8c and 8d which are not deviated, and gaps 18'a, 18'b correspond tothe gaps 8'a, 8'b which are not deviated.

FIG. 13 shows a sectional view (steel sheet 4') of the steel sheet 4deviated in a rotating direction by m° and all caulking sections 8a, 8b,8c and 8d pulled out to leave gaps. Gaps 19a, 19b, 19c and 19d of thesteel sheet 4' correspond to the caulking sections 8a. 8b, 8c and 8dwhich are not deviated, and the gaps 19'a, 19'b correspond to the gaps8'a, 8'b which are not deviated. The gaps 19a, 19b, 19c and 19d, when adie is lowered deeper to press the steel sheets, provide completelyhollow caulking sections, and when lowered shallow, provide caulkings.

FIG. 14 shows that the steel sheet 4 is caulked to the steel sheet 4"from above. The caulking sections 20d, 20a, 20b and 20c of the steelsheet 4" are placed on the gap 8'a and the caulking sections 8b, 8c and8d of the steel sheet 4. And, the steel sheet 4" can be turned in theopposite direction to place the caulking sections 20b, 20c, 20d and 20aof the steel sheet 4" on the caulking sections 8a, 8b and 8c and the gap8'b.

The gap 8'b of the steel sheet 4 is required to be put on the abovesteel sheet by turning in the opposite direction and eliminatesdirectionality in laminating the steel sheets. In addition, when thesteel sheet 4" is stacked, the permanent magnets 3, 3 for the field havethe slots 6", 6" of the steel sheet 4" held inclined with respect to theslots of the steel sheet 4 as shown in the drawing. Since theinclination of the slots slightly interfere with a part of the outerperiphery of the end faces of the permanent magnets 3, 3 for the field,magnetic fluxes substantially do not leak from the magnet end faces.Furthermore, since the permanent magnets 3, 3 for the field are insertedin the slots 6, 6 of the steel sheet 4 in the same way as in prior art,no extra force is applied to the slots. And, even when an adhesive isused to fix the permanent magnets 3, 3 for the field and the rotor isused in a refrigerant or pressurizing fluid, the dissolution of theadhesive in the refrigerant or pressurizing fluid does not cause thepermanent magnets 3, 3 for the field to come out by virtue of the steelsheet 4". Besides, the permanent magnets for the field can be fixedregardless of the processing precision of the permanent magnets for thefield.

FIG. 15 shows that the steel sheet 4 is caulked to a steel sheet 4' fromabove. In the drawing, the caulking sections 8a, 8b, 8c and 8d of thesteel sheet 4 are placed on gaps 19a, 19b, 19c and 19'b of the steelsheet 4'. The stacking of the steel sheet 4 can result in the sameeffect as in FIG. 14.

FIG. 16 shows an exploded view of the permanent magnet rotor accordingto another embodiment of the permanent magnet rotor. A yoke 2 is dividedinto two, steel sheets 4 are caulked to each steel sheet 4' from above,and these yokes 2 are moved in directions R to insert the permanentmagnets 3, 3 for the field. Positioning of the magnetic poles of eachyoke 2 is determined by the permanent magnets 3, 3 for the field and, inthis case, the positioning can be made easily because plate permanentmagnets for the field are used. Since the permanent magnets for thefield have a deviated steel sheet and slot at either end of the yokes,they do not come out by being prevented by them. And the same effect canbe obtained when the slots of the end steel sheet of the yokes have adifferent shape.

FIG. 17 shows a sectional view of the steel sheet according to anotherembodiment of the permanent magnet rotor. Slots 6, 6 are disposed inbases of magnetic poles 5a, 5b, 5c and 5d of a steel sheet 4 atsubstantially equal distance from the rotatable shaft of the yoke. Apermanent magnet for a field is inserted in these slots 6, 6.Furthermore, the steel sheet 4 has caulking sections 21a, 21b, 21c and21d formed inside of the permanent magnets for the field to mutuallypress-fit the steel sheets and gaps 22a, 22b, 22c and 22d capable ofpress-fitting the caulking sections 21a, 21b, 21c and 21d even when thesteel sheets are turned, and by turning the above caulking sections 21a,21b, 21c and 21d by m°, the caulking sections 21a, 21b, 21c and 21d arefitted in the gaps 22a, 22b, 22c and 22d. An interval m between thecaulking section 21a and the gap 22b is determined to be p×m≠360° (p isthe number of caulkings, m an interval between the caulking and thegap). And the caulking and the gap are point symmetrical with respect tothe rotatable shaft and they are on the same circumference with therotatable shaft at the center, so that the steel sheets are wellbalanced at a high-speed rotation.

FIG. 18 shows a sectional view of the steel sheet according to anotherembodiment of the permanent magnet rotor. In this embodiment, the steelsheet has caulking sections 23a, 23b, 23c and 23d and oval gaps 24a,24b, 24c and 24d capable of press-fitting the caulking sections 23a,23b, 23c and 23d by turning the steel sheet, and is laminated bymutually press-fitting the caulking sections 23a, 23b, 23c and 23d. Thecaulking sections 23a, 23c and the gaps 24b, 24d are on the samecircumference, and the caulking sections 23b, 23d and the gaps 24a, 24care on a circumference different from the above circumference, so thatthe gap area can be made long on the circumference, thus forming an ovalshape in FIG. 18. Forming the gaps to an oval shape further enables torotate at a desired very small angle. Furthermore, the caulkings and thegaps are point symmetrical with respect to the rotatable center and thesteel sheets are well balanced at a high-speed rotation. In addition,the position of the gaps and the caulkings on a plurality ofcircumferences enables to form the gaps into a desired shape, thusallowing to reduce a weight of the yoke itself. The above caulkings areround, but not limited to it. They may be a rectangular V-shapedcaulking for example. The yoke is not limited to the laminated steelsheets, but can be made of one solid metal.

FIG. 19 shows another embodiment of the permanent magnet rotor. In thisembodiment, a yoke 2 has a twist at a very small angle formed by adeviation of the pitch between the caulkings with the rotatable shaft 7aas the center, and the slots 6, 6 of the permanent magnet rotor 1 arealso deviated by a very small angle within the permanent magnet rotor 1,making it possible to fix the permanent magnets for the field; and atthe magnetic poles, the highest back electromotive force is alwaysgenerated at the circumferential center of each rotating magnetic poleface, thus allowing to hold tile-shaped permanent magnets 3, 3 in theslots 6, 6.

FIG. 20 shows an exploded view of the permanent magnet rotor accordingto another embodiment. A permanent magnet rotor 1 forms a yoke 2 bylaminating a large number of steel sheets 4 into one body by the sameway as above, the steel sheets 4 have caulking sections 8 formed bydenting them partly, and the caulking sections 8 are mutuallypress-fitted to laminate into one body. Permanent magnets 3, 3 for thefield are formed into a hexahedron having a rectangular cross section,and respectively inserted into the slots. Then a round iron sheet 25having caulking sections 8 is attached to slightly cover with its outerperiphery the permanent magnets 3, 3 for the field to integrallypress-fit by the caulking sections 8 (see FIG. 21). The structure asdescribed above allows to caulk the gaps in the yoke through apositioning pin in a rotating direction when caulking the steel sheets,preventing the permanent magnets for the field from coming out axially,and after shrinkage fitting of the yoke to the rotatable shaft, thepermanent magnets for the field can be inserted, then the iron sheet 25can be caulked last. Besides, even when an adhesive is used to fix thepermanent magnets for the field and the rotor is used in a refrigerantor pressurizing fluid, the dissolution of the adhesive in therefrigerant or pressurizing fluid does not cause the permanent magnetsfor the field to come out from the slots by virtue of the steel sheet25. And, the permanent magnets for the field can be fixed regardless ofthe processing precision of the permanent magnets for the field.

Thus, the permanent magnet rotor of the third embodiment has thedeviated steel sheet having the same shape with the steel sheets of theyoke by a pitch of the caulking at least at one end of the slots forinserting the permanent magnet for the field to enable to axially fixthe permanent magnet for the field, and can set the deviated degree ofthe steel sheets by a pitch of the caulking; this deviation can be setto a very small angle and prevents the magnetic fluxes at the end faceof the permanent magnet for the field from leaking. And, since the steelsheet at one end is deviated, it has an effect of preventing the steelsheets from falling in the axial direction. Furthermore, the gaps in thesteel sheets make it easy to press-fit and position the caulkings of thesteel sheets. Since the gaps can be formed to a desired shape, the yokeitself can be made lightweighted, and the caulkings and the gaps arepoint symmetrical with respect to the rotatable shaft, thus making theyoke well balanced. After shrinkage fitting of the yoke to the rotatableshaft, the permanent magnets for the field can be inserted easily, andafter inserting, another-shaped iron sheet can be easily fixed bycaulking with reference to the gap. In addition, since high processingprecision is not required thanks to the positional matching of the slotsand the permanent magnets for the field, the permanent magnet rotor canbe produced easily. And, the permanent magnets for the field can beprevented from coming out even when used in a refrigerant orpressurizing fluid, and the permanent magnet rotor which can be easilyproduced and assembled can be obtained.

FIG. 22 shows a perspective view of the permanent magnet rotor of afourth embodiment, and FIG. 23 shows a cross section intersecting atright angles to the rotatable shaft of the permanent magnet rotor. Thepermanent magnet rotor 1 has a pair of plate permanent magnets 3, 3 inthis case. The yoke 2 is formed by punching out a large number of steelsheets 4 by a die and laminating. The steel sheets 4 have caulkingsections 8 which are formed by partly denting the steel sheets, and arelaminated into one body by mutually press-fitting the caulking sections8. And, in this embodiment, bridges 10, 10 are produced to have a widthof 0.35 mm.

In FIG. 23, the magnetic fluxes passing through the bridges 10 do notcross the stator of a motor because they do not pass the outer space ofthe yoke 23. Therefore, a force for rotating the permanent magnet rotoris not produced. The reduction of the magnetic fluxes passing throughthe bridges 10 can use the magnetic force of the permanent magnet 3 forthe field more effectively.

The magnetic fluxes φ passing through the bridges 10 are calculated fromthe following formula. Assuming that the sectional area of the bridges10 is S and the magnetic flux density of the steel sheet 4 is B, thefollowing formula is established.

    φ=B×S

It is obvious from the above formula that the magnetic fluxes passingthrough the bridges 10 can be reduced by making the sectional area S ofthe bridges 10 smaller. On the other hand, a centrifugal breakageapplied to the bridges is calculated from the following formula.Assuming that the centrifugal force is F and the yielding point of thesteel sheet is D, the following formula is established.

    F/S<D

And, the sectional area S is calculated from the following formula. InFIG. 22, assuming that the bridge width is M, the steel sheet thicknessis T, and the yoke thickness is N, the following formula is established.

    S=M×T×(N/T)×2

It is obvious from the above formula that when the yoke length is fixed,the allowable width M should be increased according to the necessarystrength of the bridges 10. In the above formula, (N/T) is the number ofsteel sheets 4, and (×2) means that one magnetic pole has two bridges10.

FIG. 24 shows a relation among the bridge width, the magnetic fluxdensity of the bridges, and the mechanical strength of the bridges. Morespecifically, the horizontal axis shows the bridge width, and thevertical axis shows the magnetic flux density of the bridges and themechanical strength against the centrifugal force. And, curve L1indicates a magnetic flux density curve, and L2 indicates a mechanicalstrength curve against the centrifugal force. The curve L1 forms astraight line without any change between point a or a minimum widthcapable of being punched out by a die and point b or a minimum width ofan allowable magnetic flux density, and shows that the magnetic fluxdensity is gradually lowered with a width larger than the width of thepoint b.

The width of the point a capable of being punched out by a die dependson the steel sheet thickness, and the thickness is 0.1 mm, 0.35 mm or0.5 mm. And the relation of the bridge width capable of being producedby a die is expressed as M/T≧1. For example, when the steel sheetthickness is 0.35 mm and the bridge width is 0.35 mm or more, theproduction can be made easily. But, the bridge width is influenced bythe minimum width allowed from the mechanical strength against thecentrifugal force. Therefore, when the width allowed from the mechanicalstrength due to the centrifugal force is within the width capable ofbeing produced by a die, highly efficient performance with a less lossof the magnetic fluxes of the permanent magnets for the field and theminimum width capable of being produced by a die can be obtained bydetermining to either of the width capable of being produced by a die orthe width allowed from the magnetic flux density.

And, when the width allowed from the mechanical strength due to thecentrifugal force is between the width capable of being produced by adie and the width allowed from the magnetic flux density, by determiningto either of the width allowed from the mechanical strength due to thecentrifugal force or the width allowed from the magnetic flux density,highly efficient performance with a less loss of the magnetic fluxes ofthe permanent magnets for the field and capable of punching out quicklyby a die can be realized.

And, when the width allowed from the mechanical strength due to thecentrifugal force is equal to or greater than the width allowed from themagnetic flux density, the width allowed from the mechanical strengthdue to the centrifugal force is selected. In this case, it isadvantageous that the production is easy by virtue of rigidity againstthe punching out by the die and the production cost is lowered becausethe steel sheet material can be a low-saturated steel sheet material.

In summary, among the width capable of being punched out, the widthallowed in view of the number of passing magnetic fluxes, and the widthallowed from the mechanical strength due to the centrifugal force, thebridge width at either end of the slot is determined to be equal to orlarger than larger one of the width capable of being punched out or thewidth allowed from the mechanical strength due to the centrifugal forceand equal to or smaller than the width allowed in view of the number ofpassing magnetic fluxes. Exceptionally, when the width capable of beingpunched out and the width allowed from the mechanical strength due tothe centrifugal force are equal to or larger than the width allowed inview of the magnetic flux density, it is determined to be a larger oneor more between the width capable of being punched out and the widthallowed from the mechanical strength due to the centrifugal force.

FIG. 25 shows a perspective view of the permanent magnet rotor of afifth embodiment, and FIG. 26 shows a cross section intersecting atright angles to the rotatable shaft of the permanent magnet rotor. Thepermanent magnet rotor 1 has a pair of plate permanent magnets 3, 3 inthis case. The yoke 2 is formed by punching out a large number of steelsheets 4 by a die and laminating. In this embodiment, the steel sheets 4have caulking sections 8, which are formed by partly denting the steelsheets, disposed on each magnetic pole. The caulking sections 8 areformed by partly denting the steel sheet by pressing by means of a die.Therefore, each magnetic pole has gaps formed by the dented portions ofthe caulking sections 8.

In FIG. 26, arrows in the drawing show the flow of magnetic fluxesbetween each magnetic pole and stator magnetic poles. The stator 26 hasa permanent magnet rotor 3 therein, and stator magnetic poles 27 areexcited by coils not shown. Slots 6, 6 are in the bases of magneticpoles 5a, 5c of a yoke 2 and positioned at an equal distance from therotatable shaft of the yoke 2. As described above, the permanent magnets3, 3 for the field are inserted in these slots 6, 6 with the faceshaving the magnetism of N pole opposed to each other, and the magneticfluxes get out of the magnetic poles 5a, 5c of the yoke 2 due to therepulsion of the magnetic poles as shown and reach the magnetic poles5b, 5d. As a result, the magnetic poles 5a, 5c bear the magnetism of Spole, and the magnetic poles 5b, 5d the magnetism of N pole. And, theouter periphery of the yoke 2 has the four magnetic poles alternatelyhaving N and S poles.

The yoke 2 has on each magnetic pole a caulking section 8 for laminatingsteel sheets, and the flow of the magnetic fluxes of each magnetic poledetours around the caulking section 8 and reaches the magnetic pole faceof the yoke 2 as indicated by the arrows in FIG. 26. This is because thecaulking section 8 is formed by denting the steel sheet to form a spaceby the dented portion, so that the space has a low magnetic permeabilitywith respect to the steel sheet, increasing a magnetic resistance at thecaulking section 8. Therefore, the magnetic fluxes are divided to passboth sides of the caulking section 8 of the magnetic pole and notconcentrated toward the rotating direction. Thus, the back electromotiveforce generated by the magnetic fluxes is largest at the center of themagnetic pole, allowing to prevent an erroneous detection of theposition of each magnetic pole of the permanent magnet rotor.

And, the caulking section 8 disposed on the magnetic poles 5a to 5dmakes an external force difficult to be applied to bridges 10 connectingthe base and the leading end of the magnetic pole. And even when anunexpected external force is applied to the leading end of the magneticpole, the steel sheets of the yoke 2 do not suffer from the occurrenceof separation and gaps.

FIG. 27 and FIG. 28 are explanatory views of another embodiment of thepermanent magnet rotor, showing a front view and a sectional view of theyoke 2. The above embodiment has used caulkings by denting the steelsheets for connecting the steel sheets 4. But, this embodiment forms athrough hole in magnetic poles 5a, 5b, 5c and 5d, and inserts a shaft 28to connect the laminated steel sheets 4, thereby forming the yoke 2. Theshaft 28 is aluminum, stainless steel or other nonmagnetic materials toincrease a magnetic resistance at the shaft, resulting in obtaining thesame effect as in the above embodiment. In this embodiment, each end ofthe connection shaft 28 is fixed by caulking, but desired ways such asscrewing and welding can be adopted.

The connecting portion and the space of the magnetic poles 5a to 5d arenot required to be positioned at the center of the magnetic poles. Theymay be positioned on the side of the rotating direction of the rotorwith respect to the center of the magnetic pole and approached just nextto the leading end of the magnetic pole. Disposition of the space orconnecting portion on the side of the rotating direction interrupts theflow of the magnetic fluxes which are concentrated toward the rotatingdirection, thus enhancing the effect of accelerating the concentrationof the magnetic fluxes on the center of the magnetic pole. The magneticfluxes which are prevented from concentrating toward the rotatingdirection are dispersed at the space or connecting portion, and againconcentrated toward the rotating direction on the magnetic pole. But,the disposition of the space or connecting portion at the positionimmediately next to the leading end of the magnetic pole in the rotatingdirection of the rotor causes the dispersed magnetic fluxes to reach theleading end of the magnetic pole prior to concentrating toward therotating direction, resulting in concentrating the magnetic fluxes onthe center of the magnetic pole. Thus, it is more assured that anerroneous detection of the position of each magnetic pole is prevented.

The connecting portion or space is not limited to be one on eachmagnetic pole and may be disposed in more than one. The above embodimenthas been described using the rotor having the structure that the fourmagnetic poles are formed on the outer periphery of the yoke and thepermanent magnet for the field is inserted in every other magneticpoles. But, this embodiment is not limited to the above structure andcan be applied to a case that a desired even number of magnetic poles isformed and the permanent magnet for the field is inserted in eachmagnetic pole.

In the permanent magnet rotor of this embodiment, the portion forconnecting the steel sheets is disposed on each magnetic pole, so thatthe magnetic resistance at the connecting portion is increased tosuppress the concentration of the magnetic fluxes toward the rotatingdirection. And the disposition of the connecting portion on eachmagnetic pole so as to accelerate the magnetic fluxes to concentrate onthe center of each magnetic pole generates the back electromotive forcelargest at the center of the magnetic pole, thus enabling to obtain aposition sensorless brushless motor which can accurately detect theposition of the magnetic pole of the permanent magnet rotor.

Besides, the disposition of the connecting portion on each magnetic polemakes the external force hard to be transmitted to the bridgesconnecting the base and the leading end of the magnetic pole, and evenwhen the unexpected external force is applied to the leading end of themagnetic pole, the steel sheets of the yoke forming the permanent magnetrotor are prevented from suffering the occurrence of separation andgaps, thus capable of providing the permanent magnet rotor excelling instrength.

FIG. 29 is a computer-analyzed diagram showing the flow of magneticfluxes on a cross section intersecting at right angles to the rotatableshaft of the permanent magnet rotor of a three-phase, four-pole motor(24 poles) with the rotor rotating satisfactorily. It is seen from theflow of the magnetic fluxes that the magnetic pole above the permanentmagnet for the field bends the magnetic fluxes from the stator magneticpole (pole) and the magnetic fluxes from three stator magnetic polesflow to one permanent magnet for the field. Since a half of the quantityof magnetic fluxes of the magnet passes through the magnetic pole abovethe permanent magnet for the field, a width a between the permanentmagnet for the field and the outer periphery edge of the magnetic poleis preferably in a relation of (a=1.5×b) (including a case that a isalmost (1.5×b)) with respect to a width b of the stator magnetic pole.In other words, a half of the quantity of magnetic fluxes of the magnetpasses through the part a and enters 1.5 stator magnetic poles. In thecase of the above (a=1.5×b), the magnetic fluxes flow easily and do notleak many because both magnetic flux densities are equal, resulting in aremarkable motor efficiency with a less loss.

Since the width b of the stator magnetic pole is generally fixed, whenthe width a is larger than (1.5×b), the permanent magnet for the fieldis relatively close to the rotatable shaft because the gap between therotor and the stator is fixed and the magnetic pole outside thepermanent magnet for the field has a large area, reducing a gap magneticflux density outside the rotor. Furthermore, when the magnetic pole hasa large area, the bridge width is increased to retain the magnitude of acentrifugal force, increasing a loss and lowering a motor efficiency.Besides, the magnet has a long magnetic path, and a leakage quantity isincreased.

Conversely, when the width a is smaller than (1.5×b), the permanentmagnet for the field is relatively away from the rotatable shaft andapproaches to the stator, the magnetic pole outside the permanent magnetfor the field has a small area, making the magnetic fluxes difficult tobend and easy to be saturated. Thus, the magnetic flux density increasesand a loss (core loss) is increased, making the magnet demagnetizedeasily by heat.

As described above, when a is almost equal to (1.5×b), the abovedisadvantages can be remedied, and a cutoff can be disposed on the rotormagnetic poles (removing a local concentration of magnetic fluxes) to bedescribed afterward while securing the strength of the bridges. It is tobe understood that the above width a is larger than the bridge width.

FIG. 30 and FIG. 31 are computer-analyzed diagrams showing the flow ofmagnetic fluxes on a cross section intersecting at right angles to therotatable shaft of the permanent magnet rotor of a three-phase,four-pole motor (24 poles) with the rotor rotating. FIG. 30 shows therotor magnet pole with a cutoff 29, and FIG. 31 shows it without thesame. FIG. 32 and FIG. 33 are graphs showing a gap magnetic fluxdensity, corresponding to FIG. 30 and FIG. 31 respectively. When thecutoff 29 is not disposed, the magnetic fluxes concentrate on statormagnetic poles 103, 104, and 105 respectively, and the quantity ofmagnetic fluxes is in order of the magnetic flux of the magnetic pole103, the magnetic flux of the magnetic pole 104, and the magnetic fluxof the magnetic pole 105 in proportion to the passage (torque magnitude)of a current through the stator winding, the magnetic fluxes are locallysaturated, the torque between the respective stator magnetic poles isnot uniform, and the rotation of the rotor is varied.

On the other hand, when the cutoff 29 is disposed, substantially anequal quantity of magnetic fluxes enters stator magnetic poles 203, 204and 205, the magnetic fluxes do not bend extremely at the rotor magneticpoles, saturation is not much at the magnetic poles, each statormagnetic pole has the same torque, and the rotor rotates without manychanges or vibrations. FIG. 34 is a diagram showing a relation betweenthe permanent magnet rotor and the stator of a three-phase, four-polemotor (24 poles), where A is an interval between the ends of two statormagnetic poles (2 poles), and a width of the cutoff 29 corresponds tothe above interval. In other words, the angle A is a cutoff angle. InFIG. 34, a gap G at a non-cutoff part is 0.5 mm, a maximum gap B at thecutoff part is 1.3 mm, an angle of the maximum gap B from the rotorcenter is 25°, and an angle of the cutoff end part from the rotor centeris 34°. The above values are same in the cases of 12 poles and 36 polesof a three-phase, four-pole motor. In the cases of 18 poles and 36 polesof a three-phase, six-pole motor, the cutoff angle A is 16.7°, and anangle of the cutoff end part from the rotor center is 22.7°.

Industrial Applicability

This invention is suitable for a rotor of a brushless motor used forcompact disc players, various types of acoustic equipment, OA equipmentand others which need accurate rotation and durability.

We claim:
 1. A brushless motor comprising:a stator and a rotor rotatablysupported within the stator, said rotor comprising:a yoke which isformed by laminating many steel sheets so as to provide an even numberof magnetic poles projected externally and slots provided in each of orevery other said magnetic poles, a permanent magnet for a field insertedin each of said slots and having top, bottom, front, rear, and sidefaces, and protuberances provided on opposite sides of said slots andbrought into contact with the side faces of said permanent magnet forthe field forming spaces on opposite sides of said slots.
 2. A brushlessmotor comprising:a stator and a rotor rotatably supported within thestator, said rotor comprising:a yoke which is formed by laminating manysteel sheets so as to provide an even number of magnetic poles projectedexternally and slots provided in each of or every other said magneticpoles, and a permanent magnet for a field inserted in each of said slotsand having top, bottom, front, rear, and side faces, protuberancesprovided on opposite sides of said slots so as to come into contact withthe side faces of said permanent magnet for the field, and notchesdisposed on bases of said protuberances.
 3. A brushless motorcomprising:a stator and a rotor rotatably supported within the stator,said rotor comprising:a yoke which is formed by laminating many steelsheets so as to provide an even number of magnetic poles projectedexternally and having bases and leading ends, and slots in each or everyother said magnetic poles, and a permanent magnet for a field insertedin each of said slots, bridges connecting said leading ends and saidbases of the each or every other magnetic poles at opposite sides ofsaid slots, and spaces defined between said bridges and said permanentmagnet for the field inserted in said slot.
 4. A brushless motorcomprising:a stator, a rotor rotatably supported within the stator, anda rotatable shaft for rotatably supporting said rotor within the stator,said rotor comprising:a yoke which is formed by laminating many steelsheets so as to provide an even number of magnetic poles projectedexternally, and a permanent magnet for a field inserted in each magneticpole or every other magnetic poles, caulking sections provided on saidsteel sheets at angular intervals around the shaft for press-fitting thesteel sheets mutually and gaps provided in said steel sheets at apredetermined angular distance from an adjacent caulking section forengaging with the projections of the caulking sections by turning atleast one end steel sheet, said angular intervals being set to beirregular at least at one place around the rotatable shaft.
 5. Abrushless motor comprising:a stator a rotor rotatably supported withinthe stator, and a rotatable shaft for rotatably supporting said rotorwithin said stator, said rotor comprising:a yoke which is formed bylaminating many steel sheets so as to provide an even number of magneticpoles projected externally, and a permanent magnet for a field insertedin each magnetic pole or every other magnetic poles, p caulking sectionsprovided on said steel sheets at angular intervals m around saidrotatable shaft for press-fitting the steel sheets mutually, with p andm being determined to be p×m≠360°.
 6. A brushless motor comprising:astator, a rotor rotatably supported within the stator, and a rotatableshaft for rotatably supporting said rotor within said stator, said rotorcomprising:a yoke which is formed by laminating many steel sheets so asto provide an even number of magnetic poles projected externally, and apermanent magnet for a field inserted in each magnetic pole or everyother magnetic poles, p caulking sections provided on said steel sheetsfor press-fitting the steel sheets mutually and gaps provided in saidsteel sheets at angular intervals m from adjacent caulking sections forpress-fitting with the caulking sections by turning at least one endsteel sheet, with p and m being determined to be p×m≠360°.
 7. Abrushless motor comprising:a stator and a rotor rotatably supportedwithin the stator, said rotor comprising:a yoke which is formed bylaminating many steel sheets so as to provide two split yoke sectionshaving an even number of magnetic poles projected externally, and apermanent magnet for a field inserted in each magnetic pole or everyother magnetic poles, formed as one body and held at its both ends bysaid two split yoke sections whose one end is closed so as to preventsaid permanent magnet from being separated from said rotor.
 8. Abrushless motor comprising:a stator and a rotor rotatably supportedwithin the stator and having outer periphery, said rotor comprising:ayoke which is formed by laminating many steel sheets so as to provide aneven number of magnetic poles projected externally, and a permanentmagnet for a field inserted in each magnetic pole or every othermagnetic poles, a cut off face provided on said outer periphery in sucha shape that a gap magnetic flux density passing between the cutoff faceand a magnetic pole of the stator is uniform on the cutoff face therebyproviding uniform rotation.